LETTER
Reply to Chesson et al.: Carbon stable isotopes in beef differ distinctly between corporations In reply to the letter from Chesson et al. (1), the fact that we did not separate muscle from lipid in the meat servings that we analyzed is important (2). Here we present an improved calculation based on U.S. Department of Agriculture reports that a dehydrated beef patty from McDonald’s, Wendy’s, or Burger King ranges in content from 43% to 46% lipid and 54% to 57% protein (3). Using the correct values for muscle and lipid published in Bahar et al. (4), we estimated that beef with ␦13C above ⫺19.5‰ implied a ‘‘final diet of corn silage’’ (4). This result agrees with the claim of Chesson et al. (1): 71% of the burgers we sampled met this particular criterion. However, strong differences between the fast food chains were behind this trend (Fig. 1). More than 80% of McDonald’s beef and 98% of the Wendy’s beef fit this criterion. Of the beef that did not, a clear majority (74%) came from Burger King. Above the threshold that Chesson et al. (1) claim represents ⬎85% corn, 80% of these beef patties came from Wendy’s restaurants. This information appeared in table 2 in ref. 2, but we reiterate that Wendy’s food items (including fries) reflect conspicuously high corn contribution, even 1. Chesson L, Ehleringer J, Cerling T (2009) American fast food isn’t all corn-based. Proc Natl Acad Sci USA 106:E8. 2. Jahren AH, Kraft RA (2008) Carbon and nitrogen stable isotopes in fast food: Signatures of corn and confinement. Proc Natl Acad Sci USA 105:17855–17860. 3. US Department of Agriculture, Agricultural Research Service (2008) USDA National Nutrient Database for Standard Reference, Release 21, c17 www.ars.usda.gov/ba/ bhnrc/ndl. 4. Bahar B, et al, (2005) Alteration of the carbon and nitrogen stable isotope composition of beef by substitution of grass silage with maize silage. Rapid Commun Mass Spectrom 19:1937–1942.
www.pnas.org兾cgi兾doi兾10.1073兾pnas.0812302106
Fig. 1.
Distribution of carbon isotopes in beef according to corporation.
when compared with other fast food restaurants. Our results revealed the previously scientifically undocumented importance of corn in fast food production (including beef, chicken, and fries) on a national level. Hope Jahren1 and Rebecca Kraft University of Hawaii, Manoa, 1680 East West Road, Honolulu, HI 96822
Author contributions: H.J. and R.K. wrote the paper. The authors declare no conflict of interest. 1To
whom correspondence should be addressed. E-mail:
[email protected].
PNAS 兩 February 10, 2009 兩 vol. 106 兩 no. 6 兩 E9